With the development of olefin polymerization technology, the research on catalyst that is used in polymerization reaction has made a great progress, among which the high efficiency catalyst holds an important position in polyolefin catalyst field by virtue of its good polymerization performance and mature application techniques. In particular, the production and development of polyolefin resin with new structure is drawing increasingly more attention, and thus the requirement for the overall performance of the catalyst used in olefin polymerization reaction is becoming increasingly high. On the one hand, the catalyst should adapt to the production equipment, and on the other hand, the structure of the resin produced therein can be regulated and controlled. After years of research, it is demonstrated that Mg—Ti series high efficiency catalysts can meet the requirement.
At present, the Mg—Ti series high efficiency catalysts are mainly prepared through a dissolution-precipitation method. That is, a magnesium compound is dissolved in a solvent, and a corresponding catalyst can be obtained after precipitation. For example, Japanese patent 54-40293 discloses that a magnesium compound is dissolved in a titanate compound, Japanese patents 56-811 and 58-83006 disclose that a magnesium compound is dissolved in alcohol, aldehyde, amine, or carboxylic acid compounds, Japanese patent 58-19307 discloses that a magnesium compound is dissolved in an organic phosphorus compound, and Japanese patent 58-183708 discloses that a magnesium compound is dissolved in a mixed solvent of an organic epoxy compound and an organic phosphorus compound (a phosphate ester compound).
The disadvantages of grinding method can be overcome to a certain extent by the aforesaid magnesium compound dissolution method, but there are still a lot of disadvantages in this method. The activity of the catalyst that is precipitated from the magnesium compound solution disclosed by Japanese patent 54-40293, Japanese patent 58-19307, and Japanese patent 58-183708 is relatively low. Besides, the activity of the catalyst drops apparently when the polymerization time is prolonged. Moreover, the bulk density of the polymer obtained therein is relatively low.
As a result, there is still a need for the Mg—Ti series high efficiency catalyst with a good overall performance and a magnesium halide solution used for preparing the catalyst so as to further improve the technical effect of the olefin polymerization reaction.